A touch sensing apparatus is an input apparatus which is located on a front surface of a display device or in the display device to detect a finger or a person or a position of an object, which is in direct contact with or is close to a screen of the display device.
Since the touch sensing apparatus allows a user to directly touch an object displayed on the screen to perform input, it may provide a more intuitive input interface to the user and may be replaced with an input means, such as a keyboard or a mouth, which additionally connect to a display device to operate. Therefore, a use range is on a trend of being expanded in various ways.
In general, types for implementing a touch sensing apparatus are a resistive type, an optical sensing type, a capacitive type, and the like. Since the capacitive type has advantages such as ease of multi-touch sensing, a fast response speed, and excellent durability, it is recently applied to various devices.
A capacitive touch sensing apparatus may be classified as a technique of determining contact input using self-capacitance generated between a contact object and electrodes without applying a separate driving signal or a technique of being configured with two electrode layers including driving electrodes and sensing electrodes and determining contact input using a change in mutual-capacitance between driving electrodes and sensing electrodes, which is generated by contact of a contact object.
While the technique using self-capacitance is simple in circuit composition and is easy in implementation, it has a disadvantage of determining a multi-touch. The technique using mutual-capacitance has an advantage as compared with the technique using itself-capacitance in determining a multi-touch, whereas driving electrodes and sensing electrodes should be separately formed to sense touch positions.
FIG. 1 is a drawing illustrating a configuration of a typical mutual-capacitive touch sensing apparatus. A typical mutual-capacitive touch sensing apparatus 100 includes a touch screen panel 110 including a plurality of first electrodes 112 formed along a first direction and a plurality of second electrodes 114 formed along a second direction intersecting the first electrodes 112, a driving unit 121 which sequentially applies a driving signal to the first electrodes 112, a sensing unit 122 which receives a change in capacitance from the second electrodes 114 and applies a detection signal to a controller 123, and the controller 123 which receives the detection signal from the sensing unit 122 and determines a detected touch position.
The first electrodes 112 operate as driving electrodes, and the second electrodes 114 operate as sensing electrodes. Driving electrodes 112 and sensing electrodes 114 may be formed on different layers or the same layer, and may be alternately disposed to be insulated to each other and be close to each other while not being overlapped with each other.
FIG. 2 is a drawing illustrating an electrode structure of a typical touch screen panel.
For example, as shown in FIG. 2, driving electrodes 112 and sensing electrodes 114 may be formed to be close to each other in a regular pattern such as a diamond pattern. Also, since short circuits occurs in intersections of the driving electrodes 112 and the sensing electrodes 114 when the driving electrodes 112 and the sensing electrodes 114 are formed on the same layer, driving electrodes 112 or sensing electrodes 114 which are arranged on the same line connect through bridges (now shown) formed in different layers. Short circuits are prevented from occurring in connecting portions of intersected sensing electrodes 114 and driving electrodes 112.
Mutual-capacitance is formed between adjacent driving electrodes and sensing electrodes which intersect each other by the arrangement of the driving electrodes 112 and the sensing electrodes 114. Each of driving electrodes 112 and each of sensing electrodes 114 in which mutual-capacitance is formed play a role as each sensing cell for implementing touch recognition.
When a driving signal is applied from the driving unit 121 to a driving electrode 112 included in the sensing cell, a coupled detection signal is generated to a sensing electrode 114 included in the sensing cell by mutual-capacitance formed at the sensing cell.
When a driving signal is applied to a driving electrode 112 connected to each sensing cell, mutual-capacitance formed at each sensing cell is sensed through a sensing electrode 114 connected with each sensing cell.
Therefore, the driving electrode 112 to which the driving signal is applied and a plurality of adjacent sensing electrodes 114 intersecting the driving electrode 112 are configured as respective sensing cells, and mutual-capacitance is formed for each sensing cell. When there is no conductive object (a finger or a stylus) which is close to a sensing cell, there is no change in mutual capacitance (CM) formed at the sensing cell. When the conductive object is close to or in contact with a sensing cell, there is a change in mutual-capacitance. Consequently, this change leads to changing current (and/or voltage) carried to a sensing electrode 114 connected to the sensing cell.
The sensing unit 122 connected with the sensing electrodes 114 converts the change in capacitance and information (detection signal) about a position of a sensing cell into a certain format through an analog-to-digital converter (ADC) (not shown) and transmits the converted information to the controller 123. The controller 123 calculates a touch input position using this information.
Meanwhile, this mutual-capacitive touch sensing apparatus has a problem in that touch sensitivity is not kept constant in its structure according to a touch input position and a position in which each electrode is formed. FIG. 3 is a drawing illustrating a touch input region when touch input occurs on each electrode in a conventional touch sensing apparatus. Referring to FIG. 3, for example, as shown in (a) of FIG. 3, comparing sensitivity of a touch input 310 when touch input mainly occurs on a driving electrode 112 with sensitivity of a touch input 320 when touch input mainly occurs, as shown in (b) of FIG. 3, on a sensing electrode 114, the sensitivity of the touch input 320 which occurs on the sensing electrode 114 is detected to be relatively higher than that of the touch input 310 which occurs on the driving electrode 112. This is because the controller 123 receives a change in capacitance from the sensing electrodes 114. Due to this difference, there may be an error in that input sensitivity differs in a plurality of touch input of the same degree. There may be a problem in linearity of touch input.